1. Field of the Invention
This invention relates generally to chemical mechanical polishing apparatuses, and more particularly to platen designs using pressurized membranes for improved performance in chemical mechanical polishing applications.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform Chemical Mechanical Polishing (CMP) operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. Patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1 illustrates an exemplary prior art CMP system 10. The CMP system 10 in FIG. 1 is a belt-type system, so designated because the preparation surface is an endless belt 18 mounted on two drums 24 which drive the belt 18 in a rotational motion as indicated by belt rotation directional arrows 26. A wafer 12 is mounted on a wafer head 14, which is rotated in direction 16. The rotating wafer 12 is then applied against the rotating belt 18 with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied. A platen 22 is provided to stabilize the belt 18 and to provide a solid surface onto which to apply the wafer 12. Slurry 28 composing of an aqueous solution such as NH4OH or DI containing dispersed abrasive particles is introduced upstream of the wafer 12. The process of scrubbing, buffing and polishing of the surface of the wafer is achieved by using an endless polishing pad glued to belt 18. Typically, the polishing pad is composed of porous or fibrous materials and lacks fix abrasives.
FIG. 2 is a detailed view of a conventional wafer head and platen configuration 30. The wafer head and platen configuration 30 includes the wafer head 14 and the platen 22 positioned below the wafer head 14. The wafer head 14 includes a fixed retaining ring 32 that holds the wafer 12 in position below the wafer head 14. Between the wafer head 14 and the platen 22 is the polishing pad and belt 18. The polishing platen 22 is closely spaced from a polishing pad or belt 18 with a very thin air space, referred to as an xe2x80x9cair bearingxe2x80x9d, being defined between the platen 22 and the polishing pad 18. The air bearing between the platen 22 and the pad 18 has been conventionally used in an attempt to create a uniform polishing of the surface.
To maintain the air bearing, air source holes generally are formed in the platen 22 and are arranged in concentric ring patterns from the center of the platen 22 to the outer edge of the platen 22. Each ring establishes an air delivery zone where air from an air source is directed through the holes during polishing, thus establishing the air bearing. Air is exhausted past the platen edge.
With multiple air delivery zones, the air distribution profile of the air bearing can be varied radially as necessary to achieve optimal polishing by vary the polishing rate in each zone. Unfortunately, the distribution profiles of the zones are not completely independent of each other. This complicates establishing different distribution profiles for different zones.
Moreover, the air bearing is very sensitive to conditions. For example, the pressure of the air bearing varies with the gap between the pad 18 and the platen 22. Thus, if the pad 18 is pushed toward the platen 22 in one area, the pressure of all areas of the air bearing are affected, thus adding unwanted complexity to the CMP process.
In view of the foregoing, there is a need for a method that establishes greater independence of the air distribution profiles, zone to zone, thereby facilitating establishing a polishing rate in each zone independently of the other zones and, hence, improving manufacturing flexibility and functionality.
Broadly speaking, the present invention fills these needs by providing improved performance in a CMP process using a pressurized membrane as a replacement for a platen air bearing. In one embodiment, a platen for improving performance in CMP applications is disclosed. The platen includes a membrane disposed above the platen. Disposed below the membrane is a plurality of annular bladders capable of exerting force on the membrane. In this manner, zonal control is provided during the CMP process.
In another embodiment, a system for improving performance in CMP applications is disclosed. The system includes a wafer head capable of carrying a wafer, and a polishing belt positioned below the wafer head. Further included in the system is a platen having a membrane positioned below the polishing belt. The platen further includes annular bladders disposed below the membrane, which are capable of exerting force on the membrane.
A method for improving performance in CMP applications is disclosed in yet another embodiment of the present invention. Initially, a platen is provided having a membrane positioned above the platen. The platen further includes annular bladders disposed below the membrane, which are capable of exerting force on the membrane. A wafer is then applied to a polishing belt that is disposed above the platen. Further, the polishing belt is stabilized using the platen, where the membrane on the platen applies specific forces to the polishing belt utilizing the annular bladders.
Advantageously, the annular bladders of the embodiments of the present invention improve performance during a CMP process by providing increased zonal control to the pressurized membrane. Further, unlike a conventional air bearing, the pressurized membrane of the embodiments of the present invention greatly reduces the amount of air needed during the CMP process.
Moreover, a CMP process using the pressurized membrane of the present invention is not as sensitive to conditions as conventional CMP processes utilizing air bearings. Unlike air bearings, the pressure of the pressurized membrane of the present invention does not experience as great a variance as experienced by air bearings when the gap between the polishing pad and the platen varies. Thus, if the polishing pad is pushed toward the platen in one area, the pressure in other areas of the pressurized membrane are not as affected as other areas would be when utilizing an air bearing.